Hermetic refrigerant compressor and refrigerator-freezer using the same

ABSTRACT

A hermetic refrigerant compressor ( 100 ) includes a sealed container ( 101 ) in which lubricating oil ( 103 ) having a kinematic viscosity in a range of 1 to 9 mm 2 /S at 40° C. is stored, the lubricating oil ( 103 ) containing a sliding modifier that is either sulfur or a sulfur-containing compound. A compression element ( 107 ) includes a shaft part that is a crank shaft ( 108 ). In a case where a sliding surface of a main shaft ( 109 ) is a single sliding surface, a length of the single sliding surface in an axial direction is a single sliding length L, whereas in a case where the sliding surface is divided into a plurality of sliding surfaces, a length of one of the sliding surfaces in the axial direction, the one sliding surface having the least length in the axial direction among the plurality of sliding surfaces, is the single sliding length L, and a ratio L/D of the single sliding length L to an external diameter D of the main shaft ( 109 ) is less than or equal to 0.51.

TECHNICAL FIELD

The present invention relates to a hermetic refrigerant compressor foruse in, for example, a refrigerator or an air conditioner and also to arefrigerator-freezer using the hermetic refrigerant compressor.

BACKGROUND ART

In recent years, from the viewpoint of global environment conservation,the development of a high-efficient hermetic refrigerant compressor thatuses less fossil fuels has been conducted. For example, in order torealize high efficiency, it has been proposed to form various films onsliding surfaces of slide members included in the hermetic refrigerantcompressor, and to use lubricating oil having a reduced viscosity.

The hermetic refrigerant compressor includes a sealed container in whichthe lubricating oil is stored. The sealed container also accommodates anelectric element and a compression element. The compression elementincludes, as the slide members, for example, a crank shaft, a piston,and a connecting rod serving as a coupler. A main shaft of the crankshaft and a main bearing, the piston and a bore, a piston pin and theconnecting rod, and an eccentric shaft of the crank shaft and theconnecting rod, etc., form slide parts with each other.

For example, Patent Literature 1 discloses a reciprocating compressor(hermetic refrigerant compressor) using lubricating oil having a lowviscosity. The reciprocating compressor is configured such that, amongthe slide members, the piston and the connecting rod are each made of aferrous sintered material and are steam-treated, and then a steam layeris removed from the surface of the piston by cutting, whereas theconnecting rod is subjected to nitriding after being steam-treated. InPatent Literature 1, the lubricating oil used in the reciprocatingcompressor thus configured has a kinematic viscosity in the range of 3mm²/S to 10 mm²/S at 40° C.

If the lubricating oil has a low viscosity, an oil film is not easilyformed. In this respect, in the hermetic refrigerant compressordisclosed by Patent Literature 1, the surfaces of the slide membersforming the slide parts are subjected to special treatment so that evenwith the use of the lubricating oil having a low viscosity, wear orseizing of the piston and the connecting rod will be prevented.

CITATION LIST Patent Literature

PTL 1: Japanese Laid-Open Patent Application Publication No. 2011-021530

SUMMARY OF INVENTION Technical Problem

Incidentally, the crank shaft included in a hermetic refrigerantcompressor constitutes a shaft part of the compression element driven bythe electric element, and the shaft part is pivotally supported in arotatable manner by a bearing part. By reducing the sliding area of eachof the shaft part and the bearing part (pivotally supporting part),further increased efficiency can be obtained. However, reduction in thesliding area causes lowered wear resistance.

The above-described reciprocating compressor (hermetic refrigerantcompressor) disclosed by Patent Literature 1 uses the low-viscositylubricating oil, which has a kinematic viscosity in the range of 3 mm²/Sto 10 mm²/S at 40° C. However, wear resistance to be improved in PatentLiterature 1 is the wear resistance of the piston and the connectingrod, and unlike the crank shaft, the piston and the connecting rod arenot pivotally supported by the bearing part. Accordingly, in the case ofimproving the wear resistance of the piston and the connecting rod,unlike the case of the crank shaft, the sliding area of the pivotallysupporting part would not be reduced in order to achieve highefficiency.

The present invention has been made in order to solve theabove-described problems. An object of the present invention is toprovide a hermetic refrigerant compressor that makes it possible toachieve high reliability of the shaft part that is pivotally supportedby the bearing part even with the use of lubricating oil having areduced viscosity.

Solution to Problem

In order to solve the above-described problems, a hermetic refrigerantcompressor according to the present invention includes a sealedcontainer in which lubricating oil having a kinematic viscosity in arange of 1 mm²/S to 9 mm²/S at 40° C. is stored, the sealed containeraccommodating an electric element and a compression element, thecompression element being driven by the electric element and configuredto compress a refrigerant. The compression element includes: a shaftpart that is a crank shaft including a main shaft and an eccentricshaft; and a bearing part that pivotally supports the shaft part, thebearing part including a main bearing and an eccentric bearing, the mainbearing pivotally supporting the main shaft, the eccentric bearingpivotally supporting the eccentric shaft. The main shaft includes asliding surface that slides on the main bearing, the sliding surfacebeing either a single sliding surface or divided into a plurality ofsliding surfaces. In a case where the sliding surface is the singlesliding surface, a length of the single sliding surface in an axialdirection is a single sliding length L, whereas in a case where thesliding surface is divided into the plurality of sliding surfaces, alength of one of the sliding surfaces in the axial direction, the onesliding surface having the least length in the axial direction among theplurality of sliding surfaces, is the single sliding length L, and aratio L/D of the single sliding length L to an external diameter D ofthe main shaft is less than or equal to 0.51. The lubricating oilcontains a sliding modifier that is either sulfur or a sulfur-containingcompound.

According to the above configuration, the lubricating oil islow-viscosity oil; the ratio L/D of the single sliding length L to theexternal diameter D is less than or equal to 0.51 regardless of whetherthe sliding surface of the main shaft is a single sliding surface or aplurality of sliding surfaces; and the lubricating oil contains thesulfur-based sliding modifier. Owing to these features, even though thelubricating oil is low-viscosity oil and the sliding area is reducedsuch that the ratio L/D is less than or equal to 0.51, favorable wearresistance of the slide part can be realized by the sulfur-based slidingmodifier. Consequently, the hermetic refrigerant compressor can beobtained, which makes it possible to achieve high reliability of theshaft part, which is pivotally supported by the bearing part, even withthe use of the lubricating oil having a reduced viscosity.

A refrigerator-freezer according to the present invention includes arefrigerant circuit including: the hermetic refrigerant compressorconfigured as above; a radiator; a decompressor; and a heat absorber. Inthe refrigerant circuit, the hermetic refrigerant compressor, theradiator, the decompressor, and the heat absorber are connected bypiping in an annular manner.

According to the above configuration, in the hermetic refrigerantcompressor, the low-viscosity lubricating oil is used; the sliding areais reduced; and the shaft part has high reliability. Since therefrigerator-freezer includes the hermetic refrigerant compressor, whichis highly efficient and highly reliable, the power consumption of therefrigerator-freezer can be reduced, and also, the refrigerator-freezercan be made highly reliable.

The above and other objects, features, and advantages of the presentinvention will more fully be apparent from the following detaileddescription of preferred embodiments with accompanying drawings.

Advantageous Effects of Invention

The present invention is configured as described above, and has anadvantage of being able to provide a hermetic refrigerant compressorthat makes it possible to achieve high reliability of the shaft part,which is pivotally supported by the bearing part, even with the use ofthe lubricating oil having a reduced viscosity.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional view showing one example of theconfiguration of a refrigerant compressor according to an embodiment ofthe present disclosure.

FIG. 2 is a schematic side view showing one example of the configurationof a crank shaft included in the refrigerant compressor shown in FIG. 1.

FIG. 3A is a schematic diagram showing one configuration example in acase where a sliding surface of the crank shaft shown in FIG. 2 is asingle sliding surface; and FIG. 3B and FIG. 3C are schematic diagramseach showing one configuration example in a case where the slidingsurface of the crank shaft shown in FIG. 2 is divided into a pluralityof sliding surfaces.

FIG. 4 is a schematic diagram showing one example of the configurationof a refrigerator-freezer including the refrigerant compressor shown inFIG. 1.

DESCRIPTION OF EMBODIMENTS

A hermetic refrigerant compressor according to the present disclosureincludes a sealed container in which lubricating oil having a kinematicviscosity in a range of 1 mm²/S to 9 mm²/S at 40° C. is stored, thesealed container accommodating an electric element and a compressionelement, the compression element being driven by the electric elementand configured to compress a refrigerant. The compression elementincludes: a shaft part that is a crank shaft including a main shaft andan eccentric shaft; and a bearing part that pivotally supports the shaftpart, the bearing part including a main bearing and an eccentricbearing, the main bearing pivotally supporting the main shaft, theeccentric bearing pivotally supporting the eccentric shaft. The mainshaft includes a sliding surface that slides on the main bearing, thesliding surface being either a single sliding surface or divided into aplurality of sliding surfaces. In a case where the sliding surface isthe single sliding surface, a length of the single sliding surface in anaxial direction is a single sliding length L, whereas in a case wherethe sliding surface is divided into the plurality of sliding surfaces, alength of one of the sliding surfaces in the axial direction, the onesliding surface having the least length in the axial direction among theplurality of sliding surfaces, is the single sliding length L, and aratio L/D of the single sliding length L to an external diameter D ofthe main shaft is less than or equal to 0.51. The lubricating oilcontains a sliding modifier that is either sulfur or a sulfur-containingcompound.

According to the above configuration, the lubricating oil islow-viscosity oil; the ratio L/D of the single sliding length L to theexternal diameter D is less than or equal to 0.51 regardless of whetherthe sliding surface of the main shaft is a single sliding surface or aplurality of sliding surfaces; and the lubricating oil contains thesulfur-based sliding modifier. Owing to these features, even though thelubricating oil is low-viscosity oil and the sliding area is reducedsuch that the ratio L/D is less than or equal to 0.51, favorable wearresistance of the slide part can be realized by the sulfur-based slidingmodifier. Consequently, the hermetic refrigerant compressor can beobtained, which makes it possible to achieve high reliability of theshaft part, which is pivotally supported by the bearing part, even withthe use of the lubricating oil having a reduced viscosity.

In the hermetic refrigerant compressor configured as above, in the casewhere the sliding surface is divided into the plurality of slidingsurfaces, when a total of the lengths of the plurality of slidingsurfaces in the axial direction is a total sliding length Lt, a ratioLt/D of the total sliding length Lt to the external diameter D may beless than or equal to 1.26.

According to the above configuration, in the case where the slidingsurface is divided into the plurality of sliding surfaces, the slidingarea is reduced such that not only is the ratio L/D less than or equalto 0.51, but also the ratio Lt/D of the total sliding length Lt to theexternal diameter D is less than or equal to 1.26. Accordingly, in astate where the low-viscosity lubricating oil is used and the slidingarea is reduced, the wear resistance of the slide part derived from thesulfur-based sliding modifier can be more improved.

In the hermetic refrigerant compressor configured as above, the ratioL/D may be greater than or equal to 0.15.

According to the above configuration, if the ratio L/D is greater thanor equal to 0.15, the sliding area is not reduced excessively. For thisreason, in a state where the low-viscosity lubricating oil is used andthe sliding area is reduced, suitable wear resistance of the slide partcan be realized by the sulfur-based sliding modifier.

In the hermetic refrigerant compressor configured as above, the ratioLt/D may be greater than or equal to 0.3.

According to the above configuration, if the ratio Lt/D is greater thanor equal to 0.3, the sliding area is not reduced excessively even in thecase where the sliding surface is divided into the plurality of slidingsurfaces. For this reason, in a state where the low-viscositylubricating oil is used and the sliding area is reduced, suitable wearresistance of the slide part can be realized by the sulfur-based slidingmodifier.

In the hermetic refrigerant compressor configured as above, a content ofthe sliding modifier in the lubricating oil in terms of an atomic weightof sulfur may be greater than or equal to 100 ppm.

According to the above configuration, the sulfur-based sliding modifieris added to the lubricating oil, such that the sliding modifier contenttherein in terms of the atomic weight of sulfur is greater than or equalto 100 ppm. Accordingly, in a state where the low-viscosity lubricatingoil is used and the sliding area is reduced, suitable wear resistance ofthe slide part derived from the sulfur-based sliding modifier can berealized.

In the hermetic refrigerant compressor configured as above, thelubricating oil may further contain a phosphorus-based extreme-pressureadditive.

According to the above configuration, in addition to the sulfur-basedsliding modifier, the phosphorus-based extreme-pressure additive isadded to the lubricating oil, and thereby, for example, wear of theslide part can be reduced favorably.

In the hermetic refrigerant compressor configured as above, the electricelement may be inverter-driven at a plurality of operating frequencies.

According to the above configuration, in the case where the electricelement is inverter-driven, regardless of whether low-speed operation isbeing performed or high-speed operation is being performed, the wearresistance of the slide part derived from the sulfur-based slidingmodifier can be realized. Therefore, the reliability of the hermeticrefrigerant compressor can be improved.

A refrigerator-freezer according to the present disclosure includes arefrigerant circuit including: the hermetic refrigerant compressorconfigured as above; a radiator; a decompressor; and a heat absorber. Inthe refrigerant circuit, the hermetic refrigerant compressor, theradiator, the decompressor, and the heat absorber are connected bypiping in an annular manner.

According to the above configuration, in the hermetic refrigerantcompressor, the low-viscosity lubricating oil is used; the sliding areais reduced; and the shaft part has high reliability. Since therefrigerator-freezer includes the hermetic refrigerant compressor, whichis highly efficient and highly reliable, the power consumption of therefrigerator-freezer can be reduced, and also, the refrigerator-freezercan be made highly reliable.

Hereinafter, representative embodiments of the present invention aredescribed with reference to the drawings. In the drawings, the same orcorresponding elements are denoted by the same reference signs, andrepeating the same descriptions is avoided below.

Embodiment 1

[Configuration of Refrigerant Compressor]

First, a representative configuration example of a hermetic refrigerantcompressor according to Embodiment 1 of the present disclosure isspecifically described with reference to FIG. 1 and FIG. 2. FIG. 1 is aschematic sectional view showing one example of the configuration of ahermetic refrigerant compressor 100 according to Embodiment 1 of thepresent disclosure (hereinafter, the hermetic refrigerant compressor 100may be simply referred to as “refrigerant compressor 100”). FIG. 2 is aschematic side view showing one example of the configuration of a crankshaft 108, which is a shaft part included in the refrigerant compressor100.

As shown in FIG. 1, the refrigerant compressor 100 includes a sealedcontainer 101 filled with a refrigerant that is, for example, R600a.Mineral oil is stored in the bottom of the sealed container 101 aslubricating oil 103. In the present disclosure, the lubricating oil 103has a kinematic viscosity in the range of 1 mm²/S to 9 mm²/S at 40° C.It should be noted that, in Embodiment 1, although the lubricating oil103 is low-viscosity mineral oil, the lubricating oil 103 is not thuslimited as described below. Also, as described below, the lubricatingoil 103 contains at least a sulfur-based sliding modifier (or a wearinhibitor). The lubricating oil 103 may further contain anextreme-pressure additive.

The sealed container 101 also accommodates an electric element 106 and acompression element 107. The electric element 106 is constituted by astator 104 and a rotor 105. The compression element 107 is areciprocating element driven by the electric element 106. Thecompression element 107 includes, for example, the crank shaft 108, acylinder block 112, and a piston 120.

The crank shaft 108 is constituted by, also as shown in FIG. 2, a mainshaft 109 and an eccentric shaft 110. The rotor 105 is fixed to the mainshaft 109 by press-fitting. The eccentric shaft 110 is formed such thatit is eccentric with the main shaft 109. In Embodiment 1, the outerperipheral surface of the main shaft 109 of the crank shaft 108 includesa first sliding surface 111 a, a second sliding surface 111 b, and anon-sliding outer peripheral surface 111 c. In addition, an unshownoil-feeding pump is provided at the lower end of the crank shaft 108.

In Embodiment 1, for example, the cylinder block 112 is made of castiron. The cylinder block 112 forms a substantially cylindrical bore 113,and includes a main bearing 114, which pivotally supports the main shaft109 of the crank shaft 108. The inner peripheral surface of the mainbearing 114 is slidably in contact with the first sliding surface 111 aand the second sliding surface 111 b of the outer peripheral surface ofthe main shaft 109, but is not in contact with the non-sliding outerperipheral surface 111 c.

It should be noted that, as shown in FIG. 1, the eccentric shaft 110 ofthe crank shaft 108 is positioned in the upper side of the refrigerantcompressor 100, whereas the main shaft 109 of the crank shaft 108 ispositioned in the lower side of the refrigerant compressor 100.Therefore, this upper-lower positional relationship (direction) isutilized when describing positions on the crank shaft 108 herein. Forexample, the upper end of the eccentric shaft 110 faces the inner uppersurface of the sealed container 101, and the lower end of the eccentricshaft 110 is connected to the main shaft 109. The upper end of the mainshaft 109 is connected to the eccentric shaft 110, and the lower end ofthe main shaft 109 faces the inner lower surface of the sealed container101. The lower end portion of the main shaft 109 is immersed in thelubricating oil 103.

In the present disclosure, the term “sliding surface” means a surfacethat is a portion of the outer peripheral surface of the shaft part, theportion being slidably in contact with the inner peripheral surface of abearing part. The non-sliding outer peripheral surface 111 c constitutesa portion of the outer peripheral surface of the main shaft 109.However, unlike the first sliding surface 111 a and the second slidingsurface 111 b, the non-sliding outer peripheral surface 111 c is asurface that is recessed (or receding) from the sliding surfaces (thefirst sliding surface 111 a and the second sliding surface 111 b), suchthat the non-sliding outer peripheral surface 111 c is not in contactwith the inner peripheral surface of the bearing part. In other words,the portions of the main shaft 109 serving as the sliding surfaces aregreater in diameter or radius than the portion of the main shaft 109serving as the non-sliding outer peripheral surface 111 c.

The piston 120 is inserted in the bore 113 in a reciprocable manner, andthereby a compression chamber 121 is formed. A piston pin 115 having,for example, a substantially cylindrical shape is disposed parallel tothe eccentric shaft 110. The piston pin 115 is locked to a piston pinhole formed in the piston 120 in a non-rotatable manner.

A coupler 117 is, for example, constituted by an aluminum castingproduct. The coupler 117 includes an eccentric bearing 119, whichpivotally supports the eccentric shaft 110, and the coupler 117 couplesthe eccentric shaft 110 and the piston 120 via the piston pin 115. Theend face of the bore 113 is sealed by a valve plate 122.

It should be noted that, in the present disclosure, the main shaft 109and the eccentric shaft 110 included in the crank shaft 108 arecollectively referred to as the “shaft part”. Also, the main bearing 114of the cylinder block 112, which pivotally supports the main shaft 109,and the eccentric bearing 119 of the coupler 117, which pivotallysupports the eccentric shaft 110, are collectively referred to as the“bearing part”.

A cylinder head 123 forms an unshown high-pressure chamber, and is fixedto the valve plate 122 at the opposite side to the bore 113. An unshownsuction tube is fixed to the sealed container 101, and also connected tothe low-pressure side (not shown) of a refrigeration cycle, such thatthe suction tube leads the refrigerant gas into the sealed container101. A suction muffler 124 is held in a sandwiched manner between thevalve plate 122 and the cylinder head 123.

The main shaft 109 of the crank shaft 108 and the main bearing 114, thepiston 120 and the bore 113, the piston pin 115 and a connecting rod ofthe coupler 117, and the eccentric shaft 110 of the crank shaft 108 andthe eccentric bearing 119 of the coupler 117, etc., form slide partswith each other.

In the refrigerant compressor 100 thus configured, first, electric poweris supplied from an unshown commercial power supply to the electricelement 106 to cause the rotor 105 of the electric element 106 torotate. The rotor 105 causes the crank shaft 108 to rotate, andeccentric motion of the eccentric shaft 110 from the coupler 117 drivesthe piston 120 via the piston pin 115. The piston 120 makesreciprocating motion in the bore 113, sucks the refrigerant gas that hasbeen led into the sealed container 101 through the suction tube from thesuction muffler 124, and compresses the sucked refrigerant gas in thecompression chamber 121.

It should be noted that a specific method adopted herein for driving therefrigerant compressor 100 is not particularly limited. For example, therefrigerant compressor 100 may be driven by simple on-off control, ormay be inverter-driven at a plurality of operating frequencies. In thecase where the refrigerant compressor 100 is inverter-driven, in orderto optimize the operation control of the refrigerant compressor 100,low-speed operation or high-speed operation is performed. When thelow-speed operation is performed, the amount of oil fed to each slidepart decreases, whereas when the high-speed operation is performed, therotation speed of the electric element 106 increases. Here, in therefrigerant compressor 100, the wear resistance of the main shaft 109can be improved as described below. Consequently, the reliability of therefrigerant compressor 100 can be improved.

Among the plurality of slide parts included in the refrigerantcompressor 100, the main shaft 109 of the crank shaft 108 is rotatablyfitted to the main bearing 114, and thereby a slide part is formed.Therefore, for the sake of convenience of the description, the slidepart thus formed by the main shaft 109 and the main bearing 114 isreferred to as a “main shaft slide part”. Similarly, the eccentric shaft110 of the crank shaft 108 is rotatably fitted to the eccentric bearing119, and thereby a slide part is formed. Therefore, for the sake ofconvenience of the description, the slide part thus formed by theeccentric shaft 110 and the eccentric bearing 119 is referred to as an“eccentric shaft slide part”. Also, the “main shaft slide part” and the“eccentric shaft slide part” are collectively referred to as a “shaftslide part”.

In accordance with the rotation of the crank shaft 108, the oil-feedingpump feeds the lubricating oil 103 to each slide part, and thereby eachslide part is lubricated. It should be noted that the lubricating oil103 serves to seal between the piston 120 and the bore 113.

[Configuration of Shaft Slide Part]

Next, one example of a specific configuration of the shaft slide partaccording to the present disclosure is specifically described withreference to FIG. 3A to FIG. 3C. FIG. 3A is a schematic diagram showingone configuration example in a case where the sliding surface of thecrank shaft 108 shown in FIG. 2 is a single sliding surface. FIG. 3B andFIG. 3C are schematic diagrams each showing one configuration example ina case where the sliding surface of the crank shaft 108 shown in FIG. 2is divided into a plurality of sliding surfaces.

In the example shown in FIG. 2, the main shaft 109 of the crank shaft108, which is the shaft part, is configured to include the first slidingsurface 111 a and the second sliding surface 111 b. In other words, thesliding surface of the main shaft 109 is divided into a plurality ofsliding surfaces. The configuration of the main shaft 109 shown in FIG.2, i.e., the configuration in which the sliding surface is divided intotwo sliding surfaces, corresponds to the schematic diagram shown in FIG.3B. However, the shaft part according to the present disclosure is notthus limited. The sliding surface of the main shaft 109 may be a singlesliding surface. For example, as shown in FIG. 3A, the outer peripheralsurface of the main shaft 109 need not be divided into a plurality ofsliding surfaces, but instead, the main shaft 109 may have only onesliding surface 111.

A specific manner of dividing the sliding surface into a plurality ofsliding surfaces is not particularly limited. Typically, between aplurality of sliding surfaces, a recess that is recessed (or receding)from the sliding surfaces toward the center axis may be formed. Therecess constitutes the non-sliding outer peripheral surface 111 c asshown in FIG. 2 and FIG. 3B. A specific shape of the recess is notparticularly limited. For example, the depth of the recess may be set toany depth, so long as the set depth will not affect, for example, thestiffness and strength of the main shaft 109. Similarly, the width ofthe recess (i.e., the distance between the plurality of slidingsurfaces) is not particularly limited. The width of the recess can besuitably set in accordance with how much the sliding surface is to benarrowed down (i.e., in accordance with an intended reduction ordecrease in the sliding area).

In the case of dividing the sliding surface into a plurality of slidingsurfaces, the plurality of sliding surfaces is not particularly limitedto a specific number of surfaces. As shown in FIG. 2 and FIG. 3B, thesliding surface may be divided into the first sliding surface 111 a andthe second sliding surface 111 b, i.e., a total of two sliding surfaces.Alternatively, as shown in FIG. 3C, the sliding surface may be dividedinto a first sliding surface 111 d, a second sliding surface 111 e, anda third sliding surface 111 f, i.e., a total of three sliding surfaces,or may be divided into four or more sliding surfaces. In theconfiguration shown in FIG. 3C, a first non-sliding outer peripheralsurface 111 g, which is the same recess as the non-sliding outerperipheral surface 111 c, is positioned between the first slidingsurface 111 d and the second sliding surface 111 e, and a secondnon-sliding outer peripheral surface 111 h is positioned between thesecond sliding surface 111 e and the third sliding surface 111 f.

In the present disclosure, the ratio of the length of a sliding surfaceof the shaft part in the axial direction to the external diameter (thediameter) of a portion of the shaft part, the portion serving as thesliding surface, is set to less than or equal to a predetermined value,and thereby the sliding area can be reduced without substantiallyaffecting the wear resistance. Specifically, in a case where the slidingsurface is a single sliding surface (e.g., see FIG. 3A), the length ofthe single sliding surface in the axial direction is a single slidinglength L, whereas in a case where the sliding surface is divided into aplurality of sliding surfaces (e.g., FIG. 3B or FIG. 3C), the length ofone of the sliding surfaces in the axial direction, the one slidingsurface having the least length in the axial direction among theplurality of sliding surfaces, is the single sliding length L. Here,when the external diameter (the diameter) of a portion of the shaftpart, the portion serving as the sliding surface, is an externaldiameter D, the shaft part is designed such that the ratio L/D of thesingle sliding length L to the external diameter D of the shaft part isless than or equal to 0.51.

For the sake of convenience of the description of the external diameterD and the single sliding length L, FIG. 3A is illustrated such that thelength L of the single sliding surface 111 (i.e., the single slidinglength L) is greater than the external diameter D. If the length L ofthe single sliding surface 111 relative to the external diameter D isexactly as illustrated in FIG. 3A, the ratio L/D is greater than 0.51.However, in reality, for example, by forming a recess (a non-slidingouter peripheral surface) on the upper portion (the eccentric shaft 110side) or the lower portion (the lubricating oil 103 side) of the mainshaft 109 as seen from the single sliding surface 111, the ratio L/D canbe set to less than or equal to 0.51 (L/D≤0.51).

In FIG. 3B, the sliding surface is divided into the first slidingsurface 111 a and the second sliding surface 111 b. In the example shownin FIG. 3B, the length La of the upper first sliding surface 111 a inthe axial direction is less than the length Lb of the lower secondsliding surface 111 b in the axial direction (La<Lb). In this case, thefirst sliding surface 111 a is the “sliding surface having the leastlength”. Accordingly, the length La of the first sliding surface 111 ais the single sliding length L (L=La). In this example, on the firstsliding surface 111 a, the La/D is required to be less than or equal to0.51.

It should be noted that, similar to FIG. 3A, FIG. 3B is illustrated suchthat the length La of the first sliding surface 111 a is greater thanthe external diameter D for the sake of convenience of the descriptionof the external diameter D and the length La. Also in this case, theratio L/D can be set to less than or equal to 0.51 by, for example,increasing the length of the non-sliding outer peripheral surface 111 cin the axial direction or forming an unshown non-sliding outerperipheral surface (a recess) on the upper side of the first slidingsurface 111 a.

In FIG. 3C, the sliding surface is divided into the first slidingsurface 111 d, the second sliding surface 111 e, and the third slidingsurface 111 f. In the example shown in FIG. 3C, the length Le of themiddle second sliding surface 111 e in the axial direction is less thanthe length Ld of the upper first sliding surface 111 d in the axialdirection, and the length Ld is less than the length Lf of the lowerthird sliding surface 111 f in the axial direction (Le<Ld<Lf). In thiscase, the second sliding surface 111 e is the “sliding surface havingthe least length”. Accordingly, the length Le of the second slidingsurface 111 e is the single sliding length L (L=Le). In this example, onthe second sliding surface 111 e, the Le/D is required to be less thanor equal to 0.51.

In the present disclosure, the lower limit value of the ratio L/D is notparticularly limited. One preferable example of the lower limit value is0.15 or greater. Accordingly, a preferable range of the ratio L/D in thepresent disclosure is the range of 0.15 to 0.51. A more preferable lowerlimit of the ratio L/D is 0.30. A further preferable lower limit of theratio L/D is 0.42.

In a case where the ratio L/D is greater than 0.51, if low-viscosity oil(having a kinematic viscosity in the range of 1 mm²/S to 9 mm²/S at 40°C.) is used as the lubricating oil 103, even if the aforementionedsulfur-based sliding modifier, which will be described below, is addedto the lubricating oil 103, sufficient wear resistance cannot beobtained. On the other hand, in a case where the ratio L/D is less than0.15, although depending on various conditions of the shaft part, thereis a risk of the sliding surface becoming too narrow. Generallyspeaking, if the ratio L/D is greater than or equal to 0.15, the slidingarea is not reduced excessively. Therefore, even if low-viscosity oil isused as the lubricating oil 103, suitable wear resistance of the shaftslide part can be realized by the sulfur-based sliding modifier.

In the present disclosure, in a case where the sliding surface isdivided into a plurality of sliding surfaces, preferably, the ratio L/Dsatisfies not only the condition of being less than or equal to 0.51,but also the following condition: when the total of the lengths of theplurality of sliding surfaces in the axial direction is a total slidinglength Lt, the ratio Lt/D of the total sliding length Lt to the externaldiameter D is less than or equal to 1.26 (Lt/D≤1.26).

For instance, in the example shown in FIG. 3B, the sum of the length Laof the first sliding surface 111 a and the length Lb of the secondsliding surface 111 b is the total sliding length Lt (Lt=La+Lb).Therefore, in this example, it will suffice if La+Lb≤1.26. Also, in theexample shown in FIG. 3C, the sum of the length La of the first slidingsurface 111 d, the length Le of the second sliding surface 111 e, andthe length Lf of the third sliding surface 111 f is the total slidinglength Lt (Lt=Ld+Le+Lf). Therefore, in this example, it will suffice ifLd+Le+Lf≤1.26.

As described above, in a case where the sliding surface is divided intoa plurality of sliding surfaces, if the ratio L/D is less than or equalto 0.51 and the ratio Lt/D is less than or equal to 1.26, then in astate where low-viscosity oil is used as the lubricating oil 103 and thesliding area is reduced, the wear resistance of the shaft slide partderived from the sulfur-based sliding modifier can be more improved.

In the present disclosure, the lower limit value of the ratio Lt/D isnot particularly limited. One preferable example of the lower limitvalue is 0.3 or greater. Accordingly, a preferable range of the ratioLt/D in the present disclosure is 0.3 to 1.26. A more preferable lowerlimit of the ratio Lt/D is 0.60. A further preferable lower limit of theratio Lt/D is 0.99. Generally speaking, if the ratio Lt/D is greaterthan or equal to 0.3, the sliding area is not reduced excessively evenin a case where the sliding surface is divided into a plurality ofsliding surfaces. For this reason, even if low-viscosity oil is used asthe lubricating oil 103, suitable wear resistance of the shaft slidepart can be realized by the sulfur-based sliding modifier.

It should be noted that, in the examples shown in FIG. 3A to FIG. 3C,the main shaft 109 of the crank shaft 108 is referred to as the shaftpart, and the ratio L/D and the ratio Lt/D are described about the mainshaft 109. However, the present disclosure is not thus limited. The sameis true of the eccentric shaft 110. Specifically, in a case where asliding surface of the eccentric shaft 110, the sliding surface beingconfigured to slide on the eccentric bearing 119, is a single slidingsurface, the length of the single sliding surface in the axial directionis the single sliding length L, whereas in a case where the slidingsurface of the eccentric shaft 110 is divided into a plurality ofsliding surfaces, the length of one of the sliding surfaces in the axialdirection, the one sliding surface having the least length in the axialdirection among the plurality of sliding surfaces, is the single slidinglength L. In these cases, the ratio L/D of the single sliding length Lto the external diameter D of the eccentric shaft 110 is required to beless than or equal to 0.51. Also, when the total of the lengths of theplurality of sliding surfaces of the eccentric shaft 110 in the axialdirection is the total sliding length Lt, the ratio Lt/D of the totalsliding length Lt to the external diameter D of the eccentric shaft 110is required to be less than or equal to 1.26.

Therefore, in the refrigerant compressor 100 according to the presentdisclosure, at least one of the main shaft 109 and the eccentric shaft110, which constitute the shaft part, is required to have a ratio L/D ofless than or equal to 0.51. Similarly, at least one of the main shaft109 and the eccentric shaft 110 is required to have a ratio Lt/D of lessthan or equal to 1.26.

[Configuration of Lubricating Oil]

Next, a more specific configuration of the lubricating oil 103 stored inthe sealed container 101 is specifically described.

The lubricating oil 103 according to the present disclosure is notparticularly limited, so long as the lubricating oil 103 has a kinematicviscosity in the range of 1 mm²/S to 9 mm²/S at 40° C. Typically, forexample, at least one oil substance selected from the group consistingof mineral oil, alkyl benzene oil, and ester oil can be suitably used asthe lubricating oil 103. Only one of these oil substances may be used asthe lubricating oil 103, or a suitable combination of two or more of theoil substances may be used as the lubricating oil 103. The definition ofthe combination of two or more of the oil substances herein includes notonly a combination of two different oil substances that are both, forexample, mineral oils, but also a combination of, for example, at leastone oil substance that is a mineral oil and at least one oil substancethat is an alkyl benzene oil (or at least one oil substance that is anester oil).

The lubricating oil 103 according to the present disclosure contains notonly the above oil substance(s) but also the aforementioned sulfur-basedsliding modifier. The sulfur-based sliding modifier may be anysulfur-based sliding modifier, so long as the sulfur-based slidingmodifier allows the material of the shaft part (shaft part material) andsulfur to react with each other. Accordingly, the sliding modifier maybe sulfur, or may be a sulfur compound that contains sulfur and that isreactive with the shaft part material. For example, if the material ofthe shaft part is a ferrous material, then examples of sulfur compoundsusable as the sliding modifier include a sulfurized olefin, asulfide-based compound (e.g., dibenzyl disulfide (DBDS)), a xanthate, athiadiazole, a thiocarbonate, a sulfurized oil or fat, a sulfurizedester, a dithiocarbamate, and a sulfurized terpene.

The sulfur-based sliding modifier content in the lubricating oil 103 isnot particularly limited. Preferably, the sliding modifier is added tothe lubricating oil 103, such that the sliding modifier content thereinin terms of the atomic weight of sulfur is greater than or equal to 100ppm. The lower limit value of the addition amount of the slidingmodifier (i.e., the lower limit value of the sliding modifier content)being 100 ppm in terms of the atomic weight of sulfur is greater thanthe upper limit value of a general addition amount of a sulfur-basedextreme-pressure additive that will be described below.

If the sliding modifier content (the addition amount of the slidingmodifier) is less than 100 ppm in terms of the atomic weight of sulfur,although depending on various conditions, there is a risk that suitablewear resistance of the shaft slide part cannot be realized in a statewhere low-viscosity oil is used as the lubricating oil 103 and thesliding area of the shaft slide part is reduced. A preferable lowerlimit of the sulfur-based sliding modifier content is, for example,greater than or equal to 150 ppm in terms of the atomic weight ofsulfur. Also, a preferable upper limit of the sulfur-based slidingmodifier content is, for example, less than or equal to 1000 ppm, andmore preferably less than or equal to 500 ppm, in terms of the atomicweight of sulfur.

A compound that is the same as a known sulfur-based extreme-pressureadditive can be used as the sulfur-based sliding modifier in the presentdisclosure. However, alternatively, a compound that is more reactivewith the shaft part material than a known extreme-pressure additive canbe used as the sulfur-based sliding modifier in the present disclosure.Further alternatively, a known extreme-pressure additive in an amountgreater than a general addition amount (i.e., greater than a generaladditive content) may be added to the lubricating oil 103.

Generally speaking, an extreme-pressure additive is a compoundcontaining an active element such as sulfur, halogen, or phosphorus, andchemically reacts with the surface of the material of which a slide partis made (i.e., chemically reacts with a sliding surface) to form a film.The presence of the film suppresses, for example, wear, seizing, orfusion of slide members.

It is known that sulfur-containing compounds easily react with copper.For example, Reference Literature 1 (Japanese Laid-Open PatentApplication Publication No. 2006-117720) discloses that althoughsulfur-containing anti-wear agents are effective to prevent corrosionwear of a lead-containing slide member, such a sulfur-containinganti-wear agent tends to cause sulfurized corrosion of a slide memberthat contains a non-ferrous base metal different from lead, for example,copper (see paras. [0006] to [0007] of Reference Literature 1).

In the refrigerant compressor 100, copper wire is used as the winding ofthe electric element 106. Also, in a refrigerator-freezer using therefrigerant compressor 100, generally speaking, copper pipes are oftenused as refrigerant piping. As previously described, copper tends tocorrode by reacting with a sulfur-containing compound. For this reason,when using a sulfur-based extreme-pressure additive, it is necessary totake measures to avoid or hinder the corrosion of a member made ofcopper (or a copper-containing member) included in the refrigerantcompressor 100 or the refrigerator-freezer, thereby preventing loweringof the reliability thereof.

The applicant of the present application discloses, in ReferenceLiterature 2 (Japanese Patent No. 5671695), that in the case of using asulfur-based extreme-pressure additive in the refrigerator oil of arefrigerator-freezer, a sulfur-based extreme-pressure additive in whichthe number of sulfur cross-links is 3 or less is used so that thesulfur-based extreme-pressure additive will not react with copper in arefrigerant circulation passage. Preferably, a metal deactivator is usedtogether with the sulfur-based extreme-pressure additive.

In this respect, the inventors of the present invention have conducteddiligent studies including experimental verification. As a result of thestudies, they have found that in the case of using low-viscosity oil asthe lubricating oil 103 and reducing the sliding area of the shaft slidepart such that the aforementioned ratio L/D is less than or equal to0.51, not only is favorable wear resistance realized, but also thecorrosion of a member made of copper (or a copper-containing member) canbe substantially avoided by using a sulfur-based compound having higherreactivity as the sliding modifier or by increasing the adding amount ofthe sliding modifier (i.e., by increasing the sliding modifier content).

Further, in the refrigerant compressor 100 according to the presentdisclosure, a known extreme-pressure additive may be added to thelubricating oil 103 in addition to the sulfur-based sliding modifier. Aspecific extreme-pressure additive to be added to the lubricating oil103 is not particularly limited, and a known extreme-pressure additivecan be suitably used. Examples of known extreme-pressure additives thatcan be suitably used include a phosphorus-based compound, such as aphosphate ester, and a halogenated compound, such as a chlorine-basedhydrocarbon or a fluorine-based hydrocarbon. Only one of theseextreme-pressure additives may be added to the lubricating oilcomposition, or a suitable combination of two or more of theextreme-pressure additives may be added to the lubricating oilcomposition.

Among these extreme-pressure additives, a phosphorus-based compound canbe used preferably. Typical examples of the phosphorus-based compoundinclude tricresyl phosphate (TCP), tributyl phosphate (TBP), andtriphenyl phosphate (TPP). Among these, TCP is particularly preferable.In addition to the sulfur-based sliding modifier, a phosphorus-basedextreme-pressure additive may be added to the lubricating oil 103, andthereby, for example, wear of the shaft slide part can be reducedfavorably.

The amount of the extreme-pressure additive to be added to thelubricating oil composition is not particularly limited. For example, ina case where the lubricating oil 103 (oil substance) is a low-polaritysubstance such as mineral oil or alkyl benzene oil, a suitable additionamount of the extreme-pressure additive is in the range of 0.5 to 8.0%by weight, and more preferably in the range of 1 to 3% by weight.

Further, in the refrigerant compressor 100 according to the presentdisclosure, known various additives may be added to the lubricating oil103 in addition to the sliding modifier and the extreme-pressureadditive. Those known in the field of the lubricating oil 103 can besuitably used as the various additives to be added to the lubricatingoil 103. Typical examples of such additives include an oily agent, anantioxidant, an acid-acceptor, a metal deactivator, a defoaming agent,an anti-corrosive agent, and a dispersant. In other words, thelubricating oil 103 used in the refrigerant compressor 100 according tothe present disclosure is a lubricating oil composition constituted byat least the oil substance and the sliding modifier. The lubricating oilcomposition may contain an extreme-pressure additive (in particular, aphosphorus-based extreme-pressure additive), and may also contain otheradditives.

As described above, the refrigerant compressor 100 according to thepresent disclosure satisfies the following conditions: (1) thelubricating oil 103 has a kinematic viscosity in the range of 1 mm²/S to9 mm²/S at 40° C.; (2) the ratio L/D of the single sliding length L tothe external diameter D of the shaft part is less than or equal to 0.51;and (3) a sulfur-based sliding modifier is used. Further, in a casewhere the sliding surface is divided into a plurality of slidingsurfaces, the refrigerant compressor 100 preferably satisfies thefollowing condition (4): the ratio Lt/D of the total sliding length Ltto the external diameter D is less than or equal to 1.26. By satisfyingthese conditions, the shaft part and the bearing part can be lubricatedfavorably, which makes it possible to favorably suppress wear of theshaft slide part. Consequently, the reliability of the refrigerantcompressor 100 can be further improved.

It should be noted that the refrigerant compressor 100 according to thepresent disclosure may be inverter-driven at a plurality of operatingfrequencies as previously mentioned. In a case where the refrigerantcompressor 100 is inverter-driven, there are two operation modes of theelectric element 106, in one of which the electric element 106 isoperated at a low rotation speed (low-speed operation), and in the otherof which the electric element 106 is operated at a high rotation speed(high-speed operation). When the electric element 106 is operated at alow rotation speed, the amount of lubricating oil 103 supplied to theshaft slide part decreases. In the present disclosure, although thesliding area of the shaft slide part is reduced, even when the amount oflubricating oil 103 supplied to the shaft slide part decreases,favorable wear resistance can be realized.

Also, even when the rotation speed of the electric element 106 shiftsfrom the low rotation speed to the high rotation speed (i.e., even whenthe rotation speed of the electric element 106 increases), favorablewear resistance can be realized. Therefore, in a case where therefrigerant compressor 100 is inverter-driven, regardless of whether thelow-speed operation is being performed or the high-speed operation isbeing performed, the wear resistance of the shaft slide part derivedfrom the sulfur-based sliding modifier can be realized. Consequently,the reliability of the refrigerant compressor 100 can be improved, andalso, the operating efficiency can be improved.

As described above, in the refrigerant compressor 100 according to thepresent disclosure, the lubricating oil 103 is low-viscosity oil; theratio L/D of the single sliding length L to the external diameter D isless than or equal to 0.51 regardless of whether the sliding surface ofthe shaft part is a single sliding surface or a plurality of slidingsurfaces; and the lubricating oil 103 contains a sulfur-based slidingmodifier. Owing to these features, even though the lubricating oil 103is low-viscosity oil and the sliding area is reduced such that the ratioL/D is less than or equal to 0.51, favorable wear resistance of theslide part can be realized by the sulfur-based sliding modifier.Consequently, the hermetic refrigerant compressor can be obtained, whichmakes it possible to achieve high reliability of the shaft part, whichis pivotally supported by the bearing part, even with the use of thelubricating oil 103 having a reduced viscosity.

Embodiment 2

In Embodiment 2, one example of a refrigerator-freezer that includes therefrigerant compressor 100 described above in Embodiment 1 isspecifically described with reference to FIG. 4. FIG. 4 is a schematicdiagram showing a schematic configuration of the refrigerator-freezerincluding the refrigerant compressor 100 according to Embodiment 1.Therefore, in Embodiment 2, only a fundamental configuration of therefrigerator-freezer is briefly described.

As shown in FIG. 4, the refrigerator-freezer according to Embodiment 2includes, for example, a body 275, a dividing wall 278, and arefrigerant circuit 270. The body 275 is constituted by athermally-insulated box, a door, and so forth. The box is configured tohave one opening face, and the door is configured to open/close theopening of the box. The interior of the body 275 is divided by thedividing wall 278 into a product storage space 276 and a machinery room277. An unshown air feeder is provided in the storage space 276. Itshould be noted that the interior of the body 275 may be divided into,for example, spaces that are different from the storage space 276 andthe machinery room 277.

The refrigerant circuit 270 is configured to cool the inside of thestorage space 276. For example, the refrigerant circuit 270 includes therefrigerant compressor 100 described above in Embodiment 1, a radiator272, a decompressor 273, and a heat absorber 274, which are connected bypiping in an annular manner. The heat absorber 274 is disposed in thestorage space 276. Cooling heat of the heat absorber 274 is stirred bythe unshown air feeder so as to circulate inside the storage space 276as indicated by a dashed arrow in FIG. 4. In this manner, the inside ofthe storage space 276 is cooled.

As described above in Embodiment 1, the refrigerant compressor 100included in the refrigerant circuit 270 satisfies the followingconditions: (1) the lubricating oil 103 has a kinematic viscosity in therange of 1 mm²/S to 9 mm²/S at 40° C.; (2) the ratio L/D of the singlesliding length L to the external diameter D of the shaft part is lessthan or equal to 0.51; and (3) a sulfur-based sliding modifier is used.Further, in a case where the sliding surface is divided into a pluralityof sliding surfaces, the refrigerant compressor 100 preferably satisfiesthe following condition (4): the ratio Lt/D of the total sliding lengthLt to the external diameter D is less than or equal to 1.26. Bysatisfying these conditions, the reliability of the refrigerantcompressor 100 can be further improved.

As described above, the refrigerator-freezer according to Embodiment 2includes the above-described refrigerant compressor 100 according toEmbodiment 1. In the refrigerant compressor 100, the low-viscositylubricating oil 103 is used; the sliding area of the shaft slide part isreduced; and the shaft part has high reliability. Since therefrigerator-freezer includes the hermetic refrigerant compressor, whichis highly efficient and highly reliable, the power consumption of therefrigerator-freezer can be reduced, and also, the refrigerator-freezercan be made highly reliable.

It should be noted that the present invention is not limited to theembodiments described above, and various modifications can be madewithin the scope of the Claims. Embodiments obtained by suitablycombining technical means that are disclosed in different embodimentsand variations also fall within the technical scope of the presentinvention.

From the foregoing description, numerous modifications and otherembodiments of the present invention are obvious to a person skilled inthe art. Therefore, the foregoing description should be interpreted onlyas an example and is provided for the purpose of teaching the best modefor carrying out the present invention to a person skilled in the art.The structural and/or functional details may be substantially modifiedwithout departing from the spirit of the present invention.

INDUSTRIAL APPLICABILITY

As described above, the present invention makes it possible to provide arefrigerant compressor that uses low-viscosity lubricating oil and yethas excellent reliability and to provide a refrigerator-freezer usingthe refrigerant compressor. Therefore, the present invention is widelyapplicable to various equipment that uses a refrigeration cycle.

REFERENCE SIGNS LIST

-   -   100: refrigerant compressor    -   101: sealed container    -   103: lubricating oil    -   106: electric element    -   107: compression element    -   108: crank shaft    -   109: main shaft (shaft part)    -   110: eccentric shaft (shaft part)    -   111: single sliding surface    -   111 a: first sliding surface    -   111 b: second sliding surface    -   111 c: non-sliding outer peripheral surface    -   111 d: first sliding surface    -   111 e: second sliding surface    -   111 f: third sliding surface    -   111 g: first non-sliding outer peripheral surface    -   111 h: second non-sliding outer peripheral surface    -   112: cylinder block    -   114: main bearing (bearing part)    -   119: eccentric bearing (bearing part)    -   270: refrigerant circuit    -   272: radiator    -   273: decompressor    -   274: heat absorber

1. A hermetic refrigerant compressor comprising a sealed container inwhich lubricating oil having a kinematic viscosity in a range of 1 mm²/Sto 9 mm²/S at 40° C. is stored, the sealed container accommodating anelectric element and a compression element, the compression elementbeing driven by the electric element and configured to compress arefrigerant, wherein the compression element includes: a shaft part thatis a crank shaft including a main shaft and an eccentric shaft; and abearing part that pivotally supports the shaft part, the bearing partincluding a main bearing and an eccentric bearing, the main bearingpivotally supporting the main shaft, the eccentric bearing pivotallysupporting the eccentric shaft, the main shaft includes a slidingsurface that slides on the main bearing, the sliding surface beingeither a single sliding surface or divided into a plurality of slidingsurfaces, in a case where the sliding surface is the single slidingsurface, a length of the single sliding surface in an axial direction isa single sliding length L, whereas in a case where the sliding surfaceis divided into the plurality of sliding surfaces, a length of one ofthe sliding surfaces in the axial direction, the one sliding surfacehaving the least length in the axial direction among the plurality ofsliding surfaces, is the single sliding length L, and a ratio L/D of thesingle sliding length L to an external diameter D of the main shaft isless than or equal to 0.51, and the lubricating oil contains a slidingmodifier that is either sulfur or a sulfur-containing compound.
 2. Thehermetic refrigerant compressor according to claim 1, wherein in thecase where the sliding surface is divided into the plurality of slidingsurfaces, when a total of the lengths of the plurality of slidingsurfaces in the axial direction is a total sliding length Lt, a ratioLt/D of the total sliding length Lt to the external diameter D is lessthan or equal to 1.26.
 3. The hermetic refrigerant compressor accordingto claim 1, wherein the ratio L/D is greater than or equal to 0.15. 4.The hermetic refrigerant compressor according to claim 2, wherein theratio Lt/D is greater than or equal to 0.3.
 5. The hermetic refrigerantcompressor according to claim 1, wherein a content of the slidingmodifier in the lubricating oil in terms of an atomic weight of sulfuris greater than or equal to 100 ppm.
 6. The hermetic refrigerantcompressor according to claim 1, wherein the lubricating oil furthercontains a phosphorus-based extreme-pressure additive.
 7. The hermeticrefrigerant compressor according to claim 1, wherein the electricelement is inverter-driven at a plurality of operating frequencies.
 8. Arefrigerator-freezer comprising a refrigerant circuit including: thehermetic refrigerant compressor according to claim 1; a radiator; adecompressor; and a heat absorber, wherein in the refrigerant circuit,the hermetic refrigerant compressor, the radiator, the decompressor, andthe heat absorber are connected by piping in an annular manner.